Magnetic field geometry for crossed-field devices

ABSTRACT

A method of and means for generating a magnetic field in the interaction area of a cross-field device wherein the permanent magnet is positioned outside of the vacuum of the device is provided. Samarium cobalt magnet material is placed inside the cathode or sole of the device and end caps made from highpermeability material are used for pole pieces. Since the samarium cobalt is at end shield potential, no additional air gap is required.

United States Patent 1191 1111 3,843,904 Brown 1 Oct. 22, 1974 [54] MAGNETIC FIELD GEOMETRY FOR 3,346,766 10/1967 Feinstein BIS/39.71 CROSSED FIELD DEVICES 3,376,466 4/1968 Gerard 315/3971 3,588,588 6/1971 Numata 315/3971 [75] inventor: William C. Brown, Weston, Mass. [73] Assignee: The United States of America as Primary Examiner 1ame5 Lawrence represented the Secretary of the Assistant Examiner-Saxfield Chatmon, ll-

N W hi D C Attorney, Agent, or Firm-R. S. Sciascia; C. E. Vautrain, Jr. [22] Filed: Aug. 1, 1973 [21] Appl. No.: 384,850 [57] ABSTRACT A method of and means for generating a magnetic [52] U.S. Cl 3l5/39.7l, 313/157, 315/3951, field in the interaction area of a cross-field device 335/210 wherein the permanent magnet is positioned outside [51] Int. Cl. H0lj 25/50 of t va um f the device is provided. Samarium co- [58] Field of Search 315/3951, 39,71; 313/157; bait magnet material is placed inside the cathode or 335/210 sole of the device and end caps made from high-permeability material are used for pole pieces. [56] References Cit d Since the samarium cobalt is at end shield potential,

UNITED STATES PATENTS no additional air gap iS required. 2,235,517 7 Claims, 6 Drawing Figures 3/1941 Espe 313/157X r/se 76 76 /W 70 59 57 A E R F $72 a a i F P E A 63 E 64 73 64 53 2542222222 222527222,

PATENTED 00122974 $843904 sum 1 or 4 nux RETURN PATH USEFUL PORTION OF RETURN FLUX Pmmwnme m 3.8%.304

WATER CHANNEL MAGNETIC FIELD GEOMETRY FOR CROSSED-FIELD DEVICES This invention concerns crossed-field devices and, more particularly, improvements in establishing a magnetic field in the interaction area of such devices.

Crossed-field devices as presently constructed require a permanent magnet which is installed within the evacuated volume of the device. In such a position, these magnets cannot be removed for inspection or replacement without both exposing the evacuated volume and substantially taking apart the device. In conventional circuits the permanent magnets are at ground potential but the cathode and shields are at cathode potential, necessitating an appreciable air gap to eliminate arcing between the cathode pole piece and the external magnet. The permanent magnets are also unnecessarily bulky, heavy and costly. The present invention provides for generating the magnetic field of a crossedfield device by samarium cobalt permanent magnets which are removably inserted in the cathode structure of the device. These permanent magnets permit a substantial reduction in the weight and size of the device. They also reduce the total air gap required.

According to the invention, the magnetic field in the interaction area of the crossed-field microwave generator or other crossed-field device is generated by samarium cobalt magnet material which is placed inside the cathode or sole of the device. End caps made from high-permeability material are used for pole pieces, permitting a suitable magnetic field intensity to be formed within the interaction area for a variety of crossed-field devices. The samarium cobalt magnet material is at end shield potential so that an additional air gap is not required.

Accordingly, it is an object of the present invention to provide a method of and means for generating a magnetic field in the interaction area of a crossed-field device wherein the permanent magnet is positioned outside of the vacuum of the device.

It is another object of this invention to provide a method of and means for generating a magnetic field in the interaction area of a crossed-field device wherein the permanent magnets are at end shield potential so that an additional air gap is not required.

A further object of this invention is to provide a method of and means for generating a magnetic field in the interaction area of a crossed-field device wherein the size, weight, and potentially the cost of the magnet are greatly reduced as is the total air gap required in the magnetic field circuit.

A further object is to eliminate the need for a highly permeable material for a flux return path.

Other objects, advantages, and novel features of the invention will become apparent from the following detailed description thereof when considered in conjunction with the accompanying drawings in which like numerals represent like parts throughout and wherein:

FIG. 1 is a schematic drawing of the magnetic circuit of a conventional crossed-field device;

FIG. 2 is a schematic drawing of the magnetic circuit in a crossed-field device made according to the present invention;

FIG. 3 is a schematic drawing of one embodiment of the invention showing a magnetic field source configuration for a crossed-field device;

FIG. 4 is a schematic drawing of a crossed-field tube made according to the present invention with the magnetic material of the lower pole removed;

FIG. 5 is a schematic drawing of a crossed-field tube made according to the present invention showing the magnetic field source configuration of FIG. 3 inserted in the tube embodiment of FIG. 4; and

FIG. 6 is a front elevation, partly in section, of a working embodiment of an internal magnetic circuit for a crossed-field device incorporating the present invention.

Referring to FIGS. 1 and 2, a magnetic circuit 11 made according to conventional design is shown opposite a magnetic circuit 12 made according to the teachings of the present invention. In circuit 11, a pair of Al nico magnets 15 and 16 are shown positioned in opposed relation to a cathode l7 and spaced therefrom to form air gaps as indicated at 18 and 19. A pair of end shields 22 and 23 are attached to cathode l7 and a pair of pole pieces 26 and 27 are attached to magnets 15 and 16, respectively, all of these components being deployed in an evacuated volume as indicated at 28. A magnetic return path for the flux from the Alnico magnets is indicated by 29. The return path is usually made from iron or steel. An anode wall 30 and a vane 31 complete the basic components of the conventional configuration. The magnetic circuit of the present invention as shown in FIG. 2 includes a samarium cobalt magnet 35 which is positioned within the periphery of a vane 36, the permanent magnet having pole pieces 39 and 40 contiguously positioned on opposite ends and a cathode 42 which surrounds and is in contiguous contact with the periphery of magnet 35. As will be described infra, magnet 35 may be separated from pole pieces 39 and 40 and a magnetic circuit formed with magnet 35 and lower pole piece 40 separated from cathode 42 and upper pole piece 39. The return path for the flux is through the surrounding vacuum and air space. Part of the return flux provides the useful flux in the gap between the cathode and anode of the tube. In such an arrangement, the cathode, upper pole piece 39, anode 30 and vane 36 would be disposed in the vacuum while magnet 35 and lower pole piece 40 are deployed outside the vacuum. FIG. 3 illustrates schematically how this separation is accomplished to form a magnetic circuit.

In FIG. 3, the compact form of a magnetic field source made according to the invention is illustrated schematically. The elements of the source include an anode 50, north and south pole pieces 51 and 52, respectively, a cathode 53 and a permanent magnet of samarium cobalt 54 or other suitable magnet material. FIG. 4 illustrates the general structural arrangement of recent crossed-field devices which employ a largediameter, platinum cathode. The structure includes an outer vacuum-forming envelope 56 within which is positioned an anode 57, an upper pole piece 58, a cathode 59, a ceramic shield 60 and liners 61 and 62 for forming passages for the flow of coolant through the device. Segment 63 and end cap 64 of the lower pole piece are components associated with the present invention and are also preassembled as shown. Cathode 59, ceramic shield 60, envelope 56 and pole piece 58 form an evacuated enclosure which is unaffected by the insertion or removal of the elements required to complete the magnetic circuit of the device. An interior passage 65 between liners 61 and 62 is preferably used as the inlet passage for the coolant while a passage 66 between liner 61 and an extension 67 of cathode 59 form an outlet for the coolant. The lower pole piece of the magnetic field-forming couple is omitted in this figure.

Referring to FIG. 5, thecrossed-field device of FIG. 4 is duplicated and a plurality of samarium cobalt magnets 70, 71 and 72 and a lower pole piece 73 are shown inserted within lining 62 with pole piece 73 in register with endcap 64 thereof. The samarium cobalt magnets and lower pole piece 73 complete the material required to be inserted in the device to form a complete magnetic field for interaction with the anode-cathode electrical field in the area indicated at 75. Segment 63 adjoins cathode 59 and is at its potential. End cap 64 is positioned sufficiently close to segment 63 to allow the desired magnetic lines of force to span the gap between these elements of the lower pole piece. The thickness of end cap 64 may be adjusted to form an air space 76 of selected width as desired.

In FIG. 6, a practical embodiment of the invention is presented which includes a plurality of samarium cobalt magnets in layer form as indicated at 77, an upper pole 78, a lower pole 79, and a pair of bucking magnets 80 and 81 which also are formed of layers of samarium cobalt. The liners of the device form a water channel 84 for the flow of water for other coolant. A pair of pole pieces and end shields 86 and 87 complete the j A components necessary for an understanding of the embodiment. The magnetic field required in the electron beam region of the crossed-field amplifier is produced I by permanent magnets 77 in association with the high permeability pole pieces 86 and 87 and, where required, high permeability return circuits. In this embodiment as in the embodimentof FIG. 5, the samarium cobalt permanent magnets are removably placed inside the cathode structure of the device and are held in position within a cathode 88 by conventional means such as a cathode bushing 90. The high coercive force of the samarium cobalt magnets enable bucking magnets 80 81 to be used in the novel magnetic circuits to increase the magnetic field in the electron beam region. The bucking magnets may be positioned either inside the cathode structure as shown or externally around the anode of the crossed-field amplifier, in either event being placed outside of the vacuum envelope so that they may be replaced, serviced, etc., without interfering with the vacuum.

These magnetic circuits of samarium cobalt permanent magnets operate at their maximum energy production and require a minimum loss of flux leakage paths outside of the electron beam region. The pennanent magnets are positioned within the cathode structure but outside of the vacuum so that they can be inserted or removed through the large cathode bushing 90. End shields 86 and 87 are also made of high permeable material for magnetic field shaping. Bucking magnets 80 81 are positioned on poles 78 79 to direct the magnetic field into the interaction space which is indicated at 92. The height of the magnet is substantially 1.4 inches between the pole pieces and the diamenets 80' and 81, which increase the flux density in the interaction space, are 0.7 inches thick and have a diameter of 2.5 inches. The total weight of this magnetic circuit is 6 pounds and it obtains a magnetic field intensity of 2,400 gauss in the interaction space. i j

It will therefore be appreciated that the present invention greatly decreases the weight of the permanent magnet required in crossed-field devices as well as the cost of the magnet over a period of time because of the reduced weight and the reasonable cost of samarium cobalt. The invention also decreases thetube size of the device and provides for a better shaped magnetic field in specific applications. The total air gap required in the magnetic field circuit is greatly reduced over that required in conventional devices. In the conventional circuit, the magnets are at ground potential but the end shields are at cathode potential thereby necessitating an appreciable air gap to eliminate arcing between the pole pieces and the end shields. In the present invention, the magnets are at end shield potential so that an additional air gap is not required. Higher magnetic fields may be obtained where the length of the samarium cobalt magneto motive source is considerably greater than that of the air gap.

What is claimed is:

1. In a crossed-field device having a generally cylindrical cathode and an anode circumferentially disposed thereabout defining an electronic interaction area therebetween, .the improvements comprising:

means for generating the magnetomotive force necessary to provide the magnetic field of said device;

means associated with said generating means for forming a partial magnetic circuit disposed exterior of and adjacent to one end of said cathode;

means forming an evacuable envelope enclosing said interaction area and means completing said partial magnetic circuit disposed adjacent to the other end of said cathode in the region of said interaction area,

said generating means comprising a main magnet encompassed by the cathode of said device and disposed outside the vacuum envelope thereof,

whereby a compact crossed-field device is provided in which the magnetomotive force is at the potential of the cathode and is removable without affecting the vacuum envelope thereof. 3

2. The device as defined in claim 1 wherein said enveloe forming means defines a central opening of regular cross-section without said envelope and said magnet is a permanent magnet disposed in said central openmg.

3. The device as defined in claim 2 and further including means forming passages for coolant flow adjacent the interior surface of said cathode,

said permanent magnet and said means completing said partial magnetic circuit disposed interior of said means forming passages for coolant flow.

4. The device as defined in claim 3 wherein said permanent magnet is made of samarium cobalt so that a compact crossed-field device is formed whose perrnanent magnet maybe removed and replaced without affecting the evacuated volume of the device.

5. In a crossed-field device having a generally cylindrical cathode and an anode circumferentially disposed thereabout defining an electronic interaction area therebetween, the improvements comprising:

means for generating the magnetomotive force necessary to provide the magnetic field for said device;

means associated with said generating means for forming a partial magnetic circuit disposed exterior of and adjacent to one end of said cathode; said magnetic circuit formed of upper and lower pole pieces, said means associated with said generating means forming passages for coolant flow so that a compact crossed-field device is formed whose pennanent magnet may be removed and replaced without affecting the evacuated volume of the device,

said upper pole piece unitary and disposed entirely within the evacuable envelope, said lower pole piece fragmented and including a circumferential segment one end of which forms said interaction area with a corresponding end of said upper pole piece and the other end of which terminates within said cathode, a circumferential end cap spaced from and in register with said other end of said segment, and a transverse segment adjacent to and substantially contacting said end cap, means forming an evacuable envelope enclosing said partial magnetic circuit; said envelope forming means defining a central opening of regular cross-section within said envelope; means completing said partial magnetic circuit disposed adjacent to the other end of said cathode in the region of said interaction area, said generating means including a main samarium cobalt permanent magnet encompassed by the cathode of said device and disposed in said central opening so that the magnetomotive force is at the potential of the cathode; said permanent magnet and said means completing said partial magnetic circuit disposed interior of said circumferential segment disposed in said evacuable envelope,

'said circumferential end cap disposed in said passage fonning means,

said transverse segment removably received in said central opening,

whereby a compact crossed-field device is provided which has a removable permanent magnet disposed outside the evacuated envelope and in which the magnetomotive force is at the potential of the cathode.

6. A method of forming the magnetic field of a crossed-field microwave generator device having a cylindrical cathode to permit removal of the magnetic field forming material from the device without affecting the evacuated chamber thereof comprising:

forming one wall of the evacuated chamber of the device with the exterior surface of the cathode thereof;

removably positioning magnetic field forming material opposite the interior surface of the cathode and outside the evacuated chamber; and

completing a major internal portion of a flux path about the cathode by pole pieces disposed within the evacuated chamber and completing a minor external portion of the flux path by pole pieces disposed outside of the evacuated chamber so that the magnetic field forming material and the external portion of the flux path may be readily removed from the device.

7. The method of claim 6 and further including defining the area through which the magnetic field forming material and the external portion of the flux path are inserted by nonmagnetizable material; and

forming liquid coolant passages between the interior surface of the cathode and the area defining material. 

1. In a crossed-field device having a generally cylindrical cathode and an anode circumferentially disposed thereabout defining an electronic interaction area therebetween, the improvements comprising: means for generating the magnetomotive force necessary to provide the magnetic field of said device; means associated with said generating means for forming a partial magnetic circuit disposed exterior of and adjacent to one end of said cathode; means forming an evacuable envelope enclosing said interaction area and means completing said partial magnetic circuit disposed adjacent to the other end of said cathode in the region of said interaction area, said generating means comprising a main magnet encompassed by the cathode of said device and disposed outside the vacuum envelope thereof, whereby a compact crossed-field device is provided in which the magnetomotive force is at the potential of the cathode and is removable without affecting the vacuum envelope thereof.
 2. The device as defined in claim 1 wherein said enveloe forming means defines a central opening of regular cross-section without said envelope and said magnet is a permanent magnet disposed in said central opening.
 3. The device as defined in claim 2 and further including means forming passages for coolant flow adjacent the interior surface of said cathode, said permanent magnet and said means completing said partial magnetic circuit disposed interior of said means forming passages for coolant flow.
 4. The device as defined in claim 3 wherein said permanent magnet is made of samarium cobalt so that a compact crossed-field device is formed whose permanent magnet may be removed and replaced without affecting the evacuated volume of the device.
 5. In a crossed-field device having a generally cylindrical cathode and an anode circumferentially disposed thereabout defining an electronic interaction area therebetween, the improvements comprising: means for generating the magnetomotive force necessary to provide the magnetic field for said device; means associated with said generating means for forming a partial magnetic circuit disposed exterior of and adjacent to one end of said cathode; said magnetic circuit formed of upper and lower pole pieces, said means associated with said generating means forming passages for coolant flow so that a compact crossed-field device is formed whose permanent magnet may be removed and replaced without affecting the evacuated volume of the device, said upper pole piece unitary and disposed entirely within the evacuable envelope, said lower pole piece fragmented and including a circumferential segment one end of which forms said interaction area with a corresponding end of said upper pole piece and the other end of which terminates within said cathode, a circumferential end cap spaced from and in register with said other end of said segment, and a transverse segment adjacent to and substantially contacting said end cap, means forming an evacuable envelope enclosing said partial magnetic circuit; said envelope forming means defining a central opening of regular cross-section within said envelope; means completing said partial magnetic circuit disposed adjacent to the other end of said cathode in the region of said interaction area, said generating means including a main samarium cobalt permanent magnet encompassed by the cathode of said device and disposed in saiD central opening so that the magnetomotive force is at the potential of the cathode; said permanent magnet and said means completing said partial magnetic circuit disposed interior of said circumferential segment disposed in said evacuable envelope, said circumferential end cap disposed in said passage forming means, said transverse segment removably received in said central opening, whereby a compact crossed-field device is provided which has a removable permanent magnet disposed outside the evacuated envelope and in which the magnetomotive force is at the potential of the cathode.
 6. A method of forming the magnetic field of a crossed-field microwave generator device having a cylindrical cathode to permit removal of the magnetic field forming material from the device without affecting the evacuated chamber thereof comprising: forming one wall of the evacuated chamber of the device with the exterior surface of the cathode thereof; removably positioning magnetic field forming material opposite the interior surface of the cathode and outside the evacuated chamber; and completing a major internal portion of a flux path about the cathode by pole pieces disposed within the evacuated chamber and completing a minor external portion of the flux path by pole pieces disposed outside of the evacuated chamber so that the magnetic field forming material and the external portion of the flux path may be readily removed from the device.
 7. The method of claim 6 and further including defining the area through which the magnetic field forming material and the external portion of the flux path are inserted by nonmagnetizable material; and forming liquid coolant passages between the interior surface of the cathode and the area defining material. 